Two detergent-insoluble proteins of the human lymphocyte membrane are enriched in an isolated membrane fraction.

Human lymphocytes isolated from peripheral blood on Ficoll/Paque density gradients were surface-labelled by 125I/lactoperoxidase or 3H/reductive alkylation and lysed in buffer solutions containing non-ionic or amphoteric detergents (octylphenylpolyoxyethylenes, octylglucoside, cholylamidopropyldimethylammoniopropane sulfonate) under a variety of conditions. The cell lysate was fractionated by sedimentation or by density gradient centrifugation. The large majority of the labelled proteins is solubilized by the detergents. Two proteins of 45 000 and 30 000 molecular weight are the main detergent-insoluble, surface-labelled components. They can be fractionated from detergent lysates of cells in relatively pure form from the other membrane proteins and from nuclear material on density gradients. The same two proteins are specifically enriched in a membrane fraction isolated from a detergent-free cell homogenate by density gradient centrifugation. Cytoskeletal and other intracellular proteins remain associated with these two proteins when fractionated by either of these two independent methods.